1. Field of the Invention
The present invention relates to an illumination apparatus using a plurality of semiconductor light-emitting devices, such as light-emitting diode chips, as a light source thereof.
2. Description of the Related Art
Known are LED displays having a plurality of light-emitting diode chips forming a pixel, and a cover member surrounding the light-emitting diode chips.
The light-emitting diode chips are mounted in a line on a printed wiring board. The cover member has a cavity which contains light-emitting diode chips for one pixel, and a sealing material formed of synthetic resin is filled into the cavity. The light-emitting diode chips for one pixel are molded as one unitary piece with the cover member by the sealing member. For example, Japanese Patent No. 3329573 discloses an LED display having such a structure.
In the conventional LED display disclosed in the patent gazette, light-emitting diode chips forming one pixel include a blue LED chip. Blue LED chips have a sapphire substrate on which a GaN-based compound semiconductor layer is superposed. The sapphire substrate is bonded to a printed wiring board by an insulating adhesive.
According to conventional LED displays, light traveling toward the printed wiring board among blue light emitted by the blue LED chip is reflected, and thereby brightness of the blue LED chip observed on an emitted light observing surface facing the printed wiring board is increased.
Specifically, a filler such as alumina fine powder is mixed into the insulating adhesive which bonds the sapphire substrate to the printed wiring board, and thereby the insulating adhesive is formed as a white reflective layer. Thereby, emitted blue light which passes through the sapphire substrate of the blue LED chip is reflected on a surface of the insulating adhesive which also serves as a reflective layer.
In another example, a transparent adhesive which does not contain a filler is used as insulating adhesive, and a conductive material such as Al, Ni, Ag, and Pt is evaporated or superposed by plating onto a portion of the printed wiring board corresponding to a sapphire substrate, and thereby a reflective layer is formed. Thereby, emitted blue light which passes through the sapphire substrate of the blue LED chip is guided to the printed wiring board, and reflected by the reflective layer.
In conventional LED displays, to deliver light effectively, a reflective layer is formed in a part of a printed wiring board corresponding to a blue LED chip, and thereby light reflectivity of the printed wiring board is enhanced.
However, a reflective layer exists only in a part corresponding to a blue LED chip, and the area of the reflective layer is relatively small in consideration of the size of the whole LED display. Therefore, in prior art, there is a possibility that the intensity of light is insufficient when the apparatus is used as an illumination apparatus for general illumination. Therefore, there is room for improvement in respect of obtaining sufficient light for practical use.
Further, conventional LED displays require a special step of evaporating, or forming by plating, a conductive material onto a specific part of the printed wiring board, or a step of printing paste containing white filler. This requires time and labor for forming a reflective layer, and increases the manufacturing cost of the illumination apparatus.